The present invention relates generally to voltage regulators, and more particularly to a switching regulator that includes multiple power transistors.
Voltage regulators, such as DC to DC converters, are used to provide stable voltage sources for electronic systems. Efficient DC to DC converters are particularly needed for battery management in low power devices, such as laptop notebooks and cellular phones. Switching voltage regulators (or simply xe2x80x9cswitching regulatorsxe2x80x9d) are known to be an efficient type of DC to DC converter. A switching regulator generates an output voltage by converting an input DC voltage into a high frequency voltage, and filtering the high frequency input voltage to generate the output DC voltage. Specifically, the switching regulator includes a switch for alternately coupling and decoupling an input DC voltage source, such as a battery, to a load, such as an integrated circuit. An output filter, typically including an inductor and a capacitor, is coupled between the input voltage source and the load to filter the output of the switch and thus provide the output DC voltage. A controller, such as a pulse width modulator or a pulse frequency modulator, controls the switch to maintain a substantially constant output DC voltage.
In a conventional integrated switching regulator, the power switches are driven with on and off signals that have the same voltage as the voltage supply and ground, respectively. In addition, the transistors in conventional switching regulators are designed for reliable behavior under steady-state saturation conditions. Unfortunately, the long gate lengths required for reliable behavior result in large gate capacitance and resistance, resulting in large power losses and low efficiency. Moreover, driving the gates of transistors between the voltage supply voltage and ground may not be the most efficient solution.
As the complexity of integrated circuits and the power requirements for portable devices grow, there will be increasing pressure for switching regulators with extremely high efficiency. Therefore it would be advantageous to develop a switching regulator that operates with increased efficiency.
In one aspect, the invention is directed to a voltage regulator. The voltage regulator has an input terminal, an output terminal, a first transistor connecting the input terminal to an intermediate terminal, a second transistor connecting the intermediate terminal to ground, a controller that drives the first and second transistors to alternately couple the intermediate terminal between the input terminal and ground, and a filter disposed between the input terminal and the output terminal to provide a substantially DC voltage at the output terminal. The controller drives the first transistor with a first gate voltage and drives the second transistor with a second, different gate voltage.
Implementations of the invention may include the following features. The first transistor may be a PMOS transistor, and the second transistor may be an NMOS transistor. The first voltage may be larger than the second voltage. The first voltage may be substantially equal to an input voltage at the input terminal. The second gate voltage may be compatible with a logic voltage, and the first gate voltage may be greater than the logic voltage. The first transistor may include a first gate oxide layer, the second transistor may include a second gate oxide layer, and the first gate oxide layer may be thicker than the second gate oxide layer. The controller may include a first plurality of transistors in a drive train of the first transistor and a second plurality of transistors in a drive train of the second transistor. The second plurality of transistors may be driven with the second gate voltage. The first plurality of transistors may include a third transistor driven with the first gate voltage and a fourth transistor driven with the second gate voltage.
In another aspect, the invention is directed to a voltage regulator that has an input terminal, an output terminal, a transistor to intermittently couple the input terminal to the output terminal, and a filter disposed between the input terminal and the output terminal to provide a substantially DC voltage at the output terminal. The transistor includes a source, a drain, and a gate, and the transistor has a channel length between the source and the drain which is less than a channel length required for reliable behavior under steady state saturation conditions.
Implementations of the invention may include the following features. The channel length may be about 1 micron. The channel length may be shorter than a channel length specified for standard hot electron specification of 10% degradation in a one year period of operation. The transistor may be fabricated using one or more of process proximity correction and phase shift mask technology.
In another aspect, the invention is directed to a voltage regulator that has an input terminal, an output terminal, a first transistor connecting the input terminal to an intermediate terminal, a second transistor connecting the intermediate terminal to ground, a controller that drives the first and second transistors to alternately couple the intermediate terminal between the input terminal and ground, and a filter disposed between the input terminal and the output terminal to provide a substantially DC voltage at the output terminal. The first transistor includes a first gate oxide layer, and the second transistor includes a second gate oxide layer that is thinner than the first gate oxide layer.
Implementations of the invention may include the following features. The first transistor may be a PMOS transistor and the second transistor may be an NMOS transistor. The controller may drive the first transistor with a first gate voltage and drive the second transistor with a second, different gate voltage. The first voltage may be larger than the second voltage.
Advantages of the invention may include the following. The switching regulator may have a high power conversion efficiency. The power transistors of the switching regulator may be located on an integrated circuit (IC) chip, thereby reducing parasitic inductance and capacitance. The switching regulator may use fewer components, thus using less surface area of the IC chip, while maintaining a fast response and a low cost. In addition, the regulator may exhibit a smaller form factor and size, and may accept an input voltage that is compatible with external integrated circuits.